Guess asking what original games were ruined by their sequels would be too long a thread...so in the spirt of the question:
Eye of the Beholder 2 > EOB
I'm calling bogus on this for two reasons:
1) At first impression EOB2 seems to be better than EOB1, but since then I've played both games extensively... and my conclusion is that EOB1 is the better game.
EOB2 has a worse selection of NPCs, and worse NPC management than EOB1.
EOB2 is entirely linear. In fact it's the most linear of all the EOB games, there's no changing in what order you complete each section. Meanwhile EOB1 is so freeform that you can skip entire levels without even noticing it. (Even EOB3 has options on the order of playing through the levels.)
EOB2 has points of no return, areas that you can only ever enter once. EOB1 (and EOB3 for that matter) allows for free movement of every area, with locked doors barring progress being the only real obstacle.
Because of the above EOB2 has "walking dead" states, where you're screwed without even knowing it because you missed something you can't get anymore. (Obviously EOB1 doesn't.)
EOB2 also has cheesy death traps. EOB1 doesn't.
EOB2 requires a spellcaster to complete a certain quest, or the game won't progress. While an in-game workaaround exists, it was clearly added as an afterthought at the last minute and can be easily missed. By comparison EOB1 places no requirements on what character classes you can include in your party.
2) This thread asks what games make the prequel
irrelevant and pointless to play. EOB1 is still very relevant because you can transfer your party from EOB1 to EOB2. You can skip EOB1 and go straight to EOB2, but it's far better to play through EOB1 and then transfer the party to EOB2.
So yeah. EOB2 is still a good game, but it's noticeable
from EOB1.